1. Field of the Invention
The present invention relates to printers of the type which generate and print characters in response to communicated digitally encoded data.
2. History of the Prior Art
Printing has become an important if not essential part of many data processing operations. It is frequently necessary or desirable to be able to convert data within the system into recognizable characters or other indicia.
Accordingly printers have become common input/output devices in many data processing systems. Typically one or more printers are coupled to the main channel of the computer or data processing unit along with a number of input/output devices of other types. Such systems include a provision for arranging and storing data and then using the data to generate the desired graphics by way of the printer. The arranging and storing of the data is frequently accomplished within the data processing unit itself using the central processing unit and the main storage. In such systems data to be printed is fed by the data processing unit over the main channel to the printer where the data is translated into graphics produced in printed form.
Printers can comprise several different basic types in terms of the apparatus used to perform the printing. Impact type printers are like typewriters in that they utilize the physical impact of a piece of type of other mechanical representation of the desired graphics on a printable medium such as paper. Ink jet printers modulate a jet of ink as the jet is scanned across the printable medium in raster fashion. Still other printers convert the data into the desired visible graphics by modulating a beam such as an electron beam or a light beam as the beam is scanned over a surface. Examples of printers of this type include those employing the well-known cathode ray tube in which modulation of the scanning electron beam produces the desired characters on the face of the tube.
While printers of the type described have experienced significant improvement and development over the years, such printers suffer from a number of serious limitations, particularly with respect to their versatility in processing and handling the data to be printed and in their ability to adapt to different codes for the data and different graphics to be printed. For example the typical impact printer utilizes character type set on a chain and is therefore limited in the number and variety of characters that can be printed. A change in character style may require disruption of the operation of the printer while a different print chain is obtained and installed. It is frequently necessary that the data to be printed be stored and formated or otherwise processed in the data processing unit so that the printer need only have the capability of translating each group of data being fed into the printer into the corresponding characters.
One example of a printer utilizing a cathode ray tube to provide the visible graphics is shown in U.S. Pat. No. 3,729,730, Sevilla et al., DISPLAY SYSTEM, Apr. 24, 1973. In the Sevilla et al system dot patterns for the various characters to be generated by the CRT are stored in the main storage of the data processing unit together with character codes identifying the various dot patterns. As a counter within the printer determines each new character position on the printable medium, an appropriate one of the character codes identifying the character to be printed in that space is routed through the counter and into the dot patterns to provide to the CRT a dot pattern which causes printing of the desired character.
The Sevilla et al. system provides some versatility in its use of stored dot patterns to generate the desired characters, and the desirability of making the character sets represented by the dot patterns program alterable is recognized. However, like many other systems, the system of Sevilla et al is dependent on the data processing unit for the formating, storage and other handling of the data. In addition to being limited in the characters sets available, such arrangements are also limited in the coding that can be used for the data.
A further example of a system using a CRT for character display is provided by U.S. Pat. No. 3,609,743, Lasoff et al., DISPLAY UNIT, Sept. 28, 1971. In the Lasoff et al. system data to be printed is generated gy a keyboard and loaded in a storage unit, from which the data is applied to a character generator storing sets of character bits used to produce the characters on the CRT. The data can also be provided to the storage unit by a data processing unit.
An example of a system in which paper is electrostatically charged, exposed to a CRT beam, and then coated with a toner to develop the characters is provided by U.S. Pat. No. 3,634,828, Myers et al., GRAPHICAL DATA PROCESSING APPARATUS, Jan. 11, 1972. In the Myers et al. system a data processing unit sends standard templates identifying the dots within a matrix to be printed together with address codes identifying the various standard templates to a tape drive, from which the standard templates and address codes are temporarily stored. The address codes are then used to convey the standard templates to the CRT of the copying apparatus for generation of the desired characters.
U.S. Pat. No. 3,701,999, Congleton et al., COMPUTER OUTPUT LASER MICROFORM RECORDING SYSTEM, Oct. 31, 1972, provides an example of a system in which a rotating mirror having plural faces is used to scan a modulated laser beam across a printable medium in the form of a length of microfilm. Binary coded characters from a data processing unit are stored in a recirculating memory, where they are circulated once for each horizontal scan of the laser beam and made available to a character generator which successively provides a series of waveform patterns corresponding to a horizontal slice of each of the characters. The horizontal slice is recorded during each of the horizontal scans by modulating the laser beam so as to effectively synthesize the characters in a row piecewise in a vertical direction.
Accordingly it is an object of the present invention to provide a printer which is versatile and has a wide range of capabilities.
It is a further object of the invention to provide a printer which is capable of handling many of the functions of processing and storage of the print data.
It is a still further object of the invention to provide a printer in which a variety of different character sets can be used and in which such character sets can be loaded or substituted directly from the data processing unit or computer under program control.
It is a still further object of the invention to provide a printer in which the code of the data to be printed can be readily changed, in which a variety of different codes can be used, and in which a plurality of different codes can be simultaneously used to provide among other things for the printing of common characters using different codes, all under program control.
It is a still further object of the invention to provide a printer in which a given page of data stored in the printer is easily modified as it is printed to produce minor changes therein, so that plural copies of the page can be printed with minor modifications.